The present invention relates to a sheet feeding device, such as a large capacity cassette (hereinafter merely referred to as LCC), for storing a large number of sheets to be fed into a sheet processing apparatus such as an image forming apparatus.
Conventional LCCs are designed for installation beside a sheet processing apparatus and for storing sheets of size that are most frequently used. JP H09-086681A discloses an image forming apparatus provided with an LCC that has a capacity of approximately 2,000 sheets of A4-size plain paper. Sheets loaded in the LCC have long sides oriented perpendicular to a direction in which sheets are fed (hereinafter merely as the sheet feeding direction).
The LCC has a casing, and a sheet stacker mounted within the casing. The stacker is provided with a stacking plate for stacking sheets. The stacking plate is liftable within a predetermined range. Sheets stacked on the plate are sequentially fed into the apparatus, one by one from top to bottom. As stacked sheets are fed and decrease in number, the plate is raised. When sheets are to be replenished, the plate is lowered.
The stacker is detachably housed in the casing. The stacker is moved frontward out of the casing when sheets are to be replenished or currently loaded paper are to be changed to a different size or type of paper.
If the stacker moves out of the casing under its own weight, in the meanwhile, the stacker may collide with, and cause an injury to, an operator. Accordingly, the stacker needs to be tightly held in place within the casing. For this purpose, a first lock mechanism is provided that prevents movement of the stacker in the casing until a handle mounted at the front of the stacker is operated.
Also, a sheet jam or damage to the apparatus is caused by detaching the stacker from the casing for a duration of time that a sheet is being fed from the LCC to the apparatus, i.e., a sheet feeding operation is being performed. A sheet feeding operation needs to be completely stopped before the stacker is detached from the casing. Thus, a second lock mechanism is required that prevents the stacker from being moved out of the casing, even if the handle is operated, for a duration of time that a sheet feeding operation is being performed.
The two lock mechanisms, however, have the following problems. The two mechanisms take up respective spaces in the stacker and the casing, thereby causing upsizing of the LCC.
Also, when the handle is operated while a sheet feeding operation is being performed, a first lock mechanism, which is linked to the operation of the handle, is released, while a second lock mechanism, which maintains the stacker in the housed position for a duration of time that a sheet feeding operation is being performed, is kept engaged. If an operator tries to pull the stacker out of the casing with the first lock mechanism released and the second lock mechanism engaged, the operator exerts a pulling force on the second lock mechanism. Repeatedly exerted pulling force causes a failure in, or damage to, the second lock mechanism.
In light of the foregoing, a feature of the invention is to provide a sheet feeding device having a single lock mechanism that prevents a sheet stacker from moving out of a casing under its own weight or from being moved out of the casing for a duration of time that a sheet feeding operation is being performed, without causing upsizing of the device and a failure in, or damage to, the lock mechanism.